Why is there a disparity in the duration of torment or bliss in the grave among the deceased, such that the torment of some begins early, like Pharaoh, while the torment of others who die closer to the Hour is delayed, unlike the torment of Hellfire in the Hereafter where it begins for everyone at the same time?

The realm of Barzakh (definition) (the intermediary realm) differs from our world in terms of time reckoning. The deceased does not perceive time in the same way as a living person in this world. This is indicated by the noble verses which mention that on the Day of Resurrection, the criminals will swear that they did not tarry but for an hour, and that they considered their duration of stay in the world and Barzakh to be very short. Time for the deceased passes quickly. Whoever tarried for one hundred years in death will think it was but a day or part of a day. Likewise, the People of the Cave tarried for three hundred and nine years, and sleep is not the same as death. Therefore, it is not correct to measure the affairs of Barzakh and the Hereafter by the standards of this world, as this is a matter of the unseen.